Messrs. H. Nagaoka and K. Honda on Magnetostriction. 263 



the question can be deduced by means of simple experiments 

 on the effect of longitudinal pull on a ferromagnetic wire. 



As our object was not confined merely to the question of 

 magnetic stress, we were enabled, after several fruitless 

 attempts, to establish the fact that the effect of hydrostatic 

 pressure is not immeasurably small, but that there is a 

 remarkable reciprocal relation between the volume-change 

 due to magnetization and the change of magnetization by 

 compression. 



In order to settle the question of magnetostriction, we 

 measured the change of length and the effect of longitudinal 

 pull on the magnetization of iron and nickel. From the 

 different combinations of these effects, we can calculate the 

 coefficients k' and k" introduced by Kirchhoff. We are 

 thus enabled to examine the effect of stress from the strains 

 caused by magnetization and vice versa. 



The present paper will therefore be divided into the 

 following sections : — 



(1) Measurement of the change of volume and of length 



by magnetization. 



(2) Measurement of the effects of hydrostatic and transverse 

 pressures and of longitudinal pull on the magnetization 

 of iron and nickel. 



(3) Calculation of the coefficients Tcf and k" , and a com- 

 parison between theory and experiment. 



§ 1. Measurement of the Change of Volume and of Length 

 by Magnetization. 



Measurement of the Intensity of Magnetization. — We shall 

 hereafter consider the strains produced by magnetization as 

 functions of the magnetizing force and the intensity of 

 magnetization ; it will thus be necessary in the first place to 

 determine the magnetizations of the various specimens of the 

 ferromagnetics used in the present experiment. They were 

 of the following dimensions : — 



1. Ovoid of Swedish iron. 



Length of major axis = 20 cm. ; minor axis = 0*986 cm.; 

 volume = 10*1 8 c.cm. ; mass = 82 grin.; demagnetizing 

 factor N*= 0*0848. 



2. Cylinder of Lowmoor iron. 



Length=25 cm.; diameter = 0947 ; volume=17*55 

 c.cm.; mass = 136 grm.; demagnetizing factor N = 0*053. 



3. Nickel rod of square cross-section. 



Length = 26 cm.; side = 0*514 cm.; section = 0*264 

 sq. cm. ; volume = 6*86 c.cm.; mass = 58grm.; demag- 

 netizing factor N = 0*020. 



* See du Bois, Maqnetische Kreise (1894). 



U2 



